PImage myImage; //define an image object
PImage cpImage; //define a copy image
void setup(){
  myImage = loadImage("memorial.jpg"); //load it
  cpImage = loadImage("memorial.jpg"); //load the copy
  size(myImage.width,myImage.height); //size it to fit the window
  image(myImage, 0,0); //display the image
  loadPixels(); //load the pixels
}
//**********
void draw(){
}
//********* drag to simulate a paint brush
void mouseDragged(){
  for(int y=mouseY-10; y<mouseY+10; y++) //for a 10x10 brush area
    for(int x=mouseX-10; x<mouseX+10; x++){
      int xx = constrain(x,0,width-1); //do not exceed the screen
      int yy = constrain(y,0,height-1);
      //read from the copy and update the image
      pixels[yy*width+xx] = cpImage.pixels[yy*width+xx]^0x0000FF;
      //invert blue
    }
  //copy the two images
  myImage.copy(cpImage, 0,0,width,height,0,0,width,height);
  updatePixels(); //update to see the changes
}